U.S. patent application number 13/240707 was filed with the patent office on 2012-05-24 for sheet-fed duplex and sheet-fed duplex multi-color printers.
This patent application is currently assigned to MIYAKOSHI PRINTING MACHINERY CO., LTD.. Invention is credited to Hideo IZAWA, Kenji TAKAHASHI.
Application Number | 20120128395 13/240707 |
Document ID | / |
Family ID | 44999666 |
Filed Date | 2012-05-24 |
United States Patent
Application |
20120128395 |
Kind Code |
A1 |
IZAWA; Hideo ; et
al. |
May 24, 2012 |
Sheet-Fed Duplex and Sheet-Fed Duplex Multi-Color Printers
Abstract
A sheet-fed duplex printer comprises a pair of impression
cylinders 6a, 6b and first and second electrophotographic printing
units 7a and 7b. Each of the cylinders is provided on a peripheral
surface thereof with a paper gripper for gripping a sheet of paper.
The cylinders and printing units are so disposed relative to each
other and suitably operated for printing on one face of the sheet
of paper as it is conveyed following the peripheral surface of one
cylinder, and for printing on the other face of the sheet of paper
as it is conveyed following the peripheral surface of the other
cylinder. This arrangement allows high precision and high speed
printing of a sheet of paper large in size without increasing the
entire apparatus length.
Inventors: |
IZAWA; Hideo;
(Narashino-shi, JP) ; TAKAHASHI; Kenji;
(Narashino-shi, JP) |
Assignee: |
MIYAKOSHI PRINTING MACHINERY CO.,
LTD.
Narashino-shi
JP
|
Family ID: |
44999666 |
Appl. No.: |
13/240707 |
Filed: |
September 22, 2011 |
Current U.S.
Class: |
399/364 |
Current CPC
Class: |
G03G 15/231
20130101 |
Class at
Publication: |
399/364 |
International
Class: |
G03G 15/00 20060101
G03G015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2010 |
JP |
JP 212082/2010 |
Claims
1. A sheet-fed duplex printer, characterized in that it comprises:
a pair of impression cylinders each provided on a peripheral
surface thereof with a paper gripper for gripping a sheet of paper,
one of the impression cylinders being in rotational contact with
the other impression cylinder disposed downstream in a direction of
rotation of and obliquely below the one impression cylinder, the
two impression cylinders being synchronously rotated so that the
regions of rotational contact thereof both move downwards, the
sheet of paper reversing its printing face when the sheet of paper
conveyed following a peripheral surface of the one impression
cylinder is conveyed to follow that of the other impression
cylinder; a first electrophotographic printing unit is disposed
opposite to a peripheral surface area of the one impression
cylinder which area is upstream in the direction of rotation of the
one impression cylinder from the region of rotational contact
between the one and the other impression cylinder for printing on
one face of the sheet of paper being conveyed following the surface
of the one impression cylinder; and a second electrophotographic
printing unit is disposed opposite to a peripheral surface area of
the other impression cylinder which area is downstream in the
direction of rotation of the other impression cylinder from the
region of rotational contact between the one and the other
impression cylinder for printing on the other face of the sheet of
paper being conveyed following the surface of the other impression
cylinder.
2. A sheet-fed duplex multi-color printer, characterized in that it
comprises a plurality of sheet-fed duplex printers such as set
forth in claim 1 which are arranged side by side in a direction of
conveyance of the sheet of paper so that the other impression
cylinder in said sheet-fed duplex printer at an upstream side is
disposed in rotational contact with the one impression cylinder in
said sheet-fed duplex printer at a downstream side.
3. A sheet-fed duplex multi-color printer, characterized in that it
comprises at least two sheet-fed duplex two-color printers, the
sheet-fed duplex two-color printer comprising: a pair of impression
cylinders each provided on a peripheral surface thereof with a
paper gripper for gripping a sheet of paper, one of the impression
cylinders being in rotational contact with the other impression
cylinder disposed downstream in a direction of rotation of and
obliquely below the one impression cylinder, the two impression
cylinders being synchronously rotated so that the regions of
rotational contact thereof both move downwards, the sheet of paper
reversing its printing face when the sheet of paper conveyed
following a peripheral surface of the one impression cylinder is
conveyed to follow that of the other impression cylinder; a first
pair of electrophotographic printing units are disposed opposite to
peripheral surface areas of the one impression cylinder which areas
are both upstream in the direction of rotation of the one
impression cylinder from the region of rotational contact between
the one and the other impression cylinder and are shifted in
position from each other in the direction of rotation of the one
impression cylinder for printing in two colors on one face of the
sheet of paper being conveyed following the peripheral surface of
the one impression cylinder; and a second pair of
electrophotographic printing units are disposed opposite to
peripheral surface areas of the other impression cylinder which
areas are both downstream in the direction of rotation of the other
impression cylinder from the region of rotational contact between
the one and the other impression cylinder and are shifted in
position from each other in the direction of rotation of the other
impression cylinder for printing in the two colors on the other
face of the sheet of paper being conveyed following the peripheral
surface of the other impression cylinder; wherein at least two said
sheet-fed duplex two-color printers are arranged side by side in a
direction of conveyance of the sheet of paper so that the other
impression cylinder in said sheet-fed duplex two-color printer
positioned upstream in the direction of conveyance of the sheet of
paper and the one impression cylinder in said sheet-fed duplex
two-color printer positioned downstream in the direction of
conveyance of the sheet of paper are rotationally coupled with each
other via a pair of bridge rollers which are disposed in rotational
contact with each other and with the other and the one impression
cylinder, respectively.
Description
TECHNICAL FIELD
[0001] The present invention relates to a sheet-fed duplex and a
sheet-fed duplex multi-color printer that is designed to effect
printing on each of the front and rear faces of a sheet of paper in
a single color or a plurality of colors, using electrophotographic
printing units.
BACKGROUND ART
[0002] A machine for effecting printing, e.g., on one of the two
faces of a sheet of paper in four colors, using a plurality of
electrophotographic printing units is known as shown in JP
H07-271107 A.
[0003] In such a printer using a plurality of electrophotographic
printing units, a plurality of toner image forming units are
arranged in a direction of conveyance of a sheet of paper. Each of
the toner image forming units comprises a photoconductor drum as a
image supporting member, a charging means for charging a surface of
the photoconductor drum, an exposure means for exposing the surface
of the photoconductor drum to form a latent image on the surface
and a developing means for developing the latent image into a toner
image, or the like. Toner images formed on the respective
photoconductor drums in the toner image forming units are
successively transferred onto the sheet of paper by means of a
transfer means using a transfer conveyer belt with which the
photoconductor drums in the respective toner image forming units
are in rotational contact and the sheet of paper is conveyed.
[0004] In the conventional printer using a plurality of
electrophotographic printers, a sheet of paper is successively
conveyed on the transfer conveyer belt along a plurality of the
successive toner image forming units. Then, while being conveyed
across two adjacent toner image forming units, the sheet of paper
is nipped to be applied with printing pressure in two areas at both
end portions of the sheet of paper extending in its straight
conveyance direction, giving rise to the problem that the accuracy
in printing registration may be affected. In a multi-color printer
to prevent this problem, the spacing between adjacent toner image
forming units has been sized so that a sheet of paper after passing
through a nip portion in a toner image forming unit is fed into
that in a next toner image forming unit
[0005] Also, a printer using an electrophotographic printing unit,
development of an image onto a surface of a photoconductor drum and
cleaning of the surface of the photoconductor drum having
transferred the image can proceed always simultaneously. Thus, a
sheet of paper can be printed with a pattern of a length in its
conveyance direction regardless of a circular peripheral length of
the photoconductor drum, and even with a pattern of a length
exceeding the circular peripheral length of the photoconductor
drum. If, however, sheets of paper are to be printed with such a
long pattern, the spacing between adjacent toner image forming
units must be of a size exceeding the maximum pattern size
(length). As a result, the entire multi-color printer in which a
plurality of the toner image forming units are interconnected must
be correspondingly made longer in total size.
[0006] If in such a printer a sheet of paper is to be printed on
its both faces, a sheet of paper having been printed on its one
face by one printing unit is reversed in printing face and then
passed into a next, identical printing unit disposed adjacent
thereto. If the sheet of paper is to be printed on its front and
rear faces in four color, the length from the first toner image
forming unit to the eighth toner image forming unit must be 7
(seven) times longer than a pattern size (length). The problem thus
arises that the entire multi-color printer is made longer to allow
printing a pattern that is long in the direction of conveyance of
the sheet of paper.
[0007] Further, since the conventional printers adopt a belt
conveyer system, there have been errors in sheet feed due to
stretchability of the belt and limitations in accuracy arising from
the structural phase of the belt conveyer system, which are more
remarkable especially as the printing speed is to be increased.
There have thus existed problems in maintaining high precision in
printing registration in high speed sheet conveyance.
[0008] In view of the foregoing, it is an object of the present
invention to provide a sheet-fed duplex and a sheet-fed duplex
multi-color printer which is compact, using an electrophotographic
printing system and which, if for a long pattern to be printed on
both faces of a sheet of paper, allows producing a printed matter
at high efficiency and high precision.
DISCLOSURE OF THE INVENTION
[0009] In order to achieve the object mentioned above, there is
provided in accordance with the present invention a sheet-fed
duplex printer which comprises: a pair of impression cylinders each
provided on a peripheral surface thereof with a paper gripper for
gripping a sheet of paper, one of the impression cylinders being in
rotational contact with the other impression cylinder disposed
downstream in a direction of rotation of and obliquely below the
one impression cylinder, the two impression cylinders being
synchronously rotated so that the regions of rotational contact
thereof both move downwards, the sheet of paper reversing its
printing face when the sheet of paper conveyed following a
peripheral surface of the one impression cylinder is conveyed to
follow that of the other impression cylinder; a first
electrophotographic printing unit is disposed opposite to a
peripheral surface area of the one impression cylinder which area
is upstream in the direction of rotation of the one impression
cylinder from the region of rotational contact between the one and
the other impression cylinder for printing on one face of the sheet
of paper being conveyed following the surface of the one impression
cylinder; and a second electrophotographic printing unit is
disposed opposite to a peripheral surface area of the other
impression cylinder which area is down-stream in the direction of
rotation of the other impression cylinder from the region of
rotational contact between the one and the other impression
cylinder for printing on the other face of the sheet of paper being
conveyed following the surface of the other impression
cylinder.
[0010] There is also provided in accordance with the present
invention a sheet-fed duplex multi-color printer which comprises a
plurality of sheet-fed duplex printers such as set forth above
which are arranged side by side in a direction of conveyance of the
sheet of paper so that the other impression cylinder in the
sheet-fed duplex printer at an upstream side is disposed in
rotational contact with the one impression cylinder in the
sheet-fed duplex printer at a downstream side.
[0011] There is further provided in accordance with the present
invention an alternative sheet-fed duplex multi-color printer which
comprises at least two sheet-fed duplex two-color printers, the
sheet-fed duplex two-color printer comprising: a pair of impression
cylinders each provided on a peripheral surface thereof with a
paper gripper for gripping a sheet of paper, one of the impression
cylinders being in rotational contact with the other impression
cylinder disposed downstream in a direction of rotation of and
obliquely below the one impression cylinder, the two impression
cylinders being synchronously rotated so that the regions of
rotational contact thereof both move downwards, the sheet of paper
reversing its printing face when the sheet of paper conveyed
following a peripheral surface of the one impression cylinder is
conveyed to follow that of the other impression cylinder; a first
pair of electrophotographic printing units are disposed opposite to
peripheral surface areas of the one impression cylinder which areas
are both upstream in the direction of rotation of the one
impression cylinder from the region of rotational contact between
the one and the other impression cylinder and are shifted in
position from each other in the direction of rotation of the one
impression cylinder for printing in two colors on one face of the
sheet of paper being conveyed following the peripheral surface of
the one impression cylinder; and a second pair of
electrophotographic printing units are disposed opposite to
peripheral surface areas of the other impression cylinder which
areas are both downstream in the direction of rotation of the other
impression cylinder from the region of rotational contact between
the one and the other impression cylinder and are shifted in
position from each other in the direction of rotation of the other
impression cylinder for printing in the two colors on the other
face of the sheet of paper being conveyed following the peripheral
surface of the other impression cylinder; wherein at least two the
sheet-fed duplex two-color printers are arranged side by side in a
direction of conveyance of the sheet of paper so that the other
impression cylinder in a sheet-fed duplex two-color printer
positioned upstream in the direction of conveyance of the sheet of
paper and the one impression cylinder in a sheet-fed duplex
two-color printer positioned downstream in the direction of
conveyance of the sheet of paper are rotationally coupled with each
other via a pair of bridge rollers which are disposed in rotational
contact with each other and with the other and the one impression
cylinder, respectively.
[0012] According to the sheet-fed duplex printer of the present
invention, a sheet of paper is conveyed in the form of S character
over from the impression cylinder upstream, to the impression
cylinder downstream, in the sheet conveyance direction, making it
possible to lengthen the path of sheet conveyance over and between
the two impression cylinders while shortening the horizontal length
of the printer to effect printing of the sheet of paper, and thus
to make the printer compact. Also, since the system for conveying a
sheet of paper uses impression cylinders each provided with a paper
gripper, the sheet of paper being conveyed is made stable in
behavior, allowing high precision and high speed printing.
[0013] Further, as use is made of electrophotographic printing
units as means for printing of a sheet of paper, the output control
of image pattern data allows details of a pattern and the number of
sheets of paper or the like to be freely controlled, making it
possible to efficiently produce lots from large to small with a
compact apparatus makeup. Also, like printing data are available,
readiness time is made unnecessary, allowing the delivery of
ordered products in a shortened time limit and highly improving the
efficiency in operability. Further, the details of a pattern and
the number of sheets of paper for an identical pattern can be made
variable by digital printing in the course of continuous printing.
It is also possible to meet with printing on demand and printing of
sheets of paper sized from small to large.
[0014] According to the sheet-fed duplex multi-color printer using
sheet-fed duplex printers as mentioned above, the entire apparatus
despite being a multi-color printer can be shorted in total length,
it is possible to achieve economical advantages such as space
saving and reduction in apparatus cost.
[0015] Also, according to the alternative sheet-fed duplex
multi-color printer mentioned above, it is possible for a sheet of
paper to be printed on its both faces each in two colors with two
impression cylinders, further reducing the apparatus makeup in
size.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In the Drawings:
[0017] FIG. 1 is a structural explanatory view diagrammatically
illustrating an embodiment of the sheet-fed duplex multi-color
printer according to the present invention;
[0018] FIG. 2 is a structural explanatory view illustrating an
embodiment of the sheet-fed duplex printer according to the present
invention;
[0019] FIG. 3 is a diagrammatic view illustrating how one of the
two faces of a sheet of paper is printed by a sheet-fed duplex
printer;
[0020] FIG. 4 is an explanatory view illustrating a distance of
movement of a sheet of paper when one of its faces is printed with
one impression cylinder; and
[0021] FIG. 5 is a structural explanatory view diagrammatically
illustrating an alternative embodiment of the sheet-fed duplex
multi-color printer according to the present invention
BEST MODES FOR CARRYING OUT THE INVENTION
[0022] Mention is now made of one form of implementation of the
present invention with reference to Drawing Figures.
[0023] FIG. 1 is an explanatory view diagrammatically illustrating
a sheet-fed duplex multi-color printer 1 constructed to print on
the two faces of a sheet of paper, each in four colors. The
sheet-fed duplex multi-color printer 1 is of the makeup that a
first, a second, a third and a fourth sheet-fed duplex printer 2a,
2b, 2c and 2d are arranged side by side in a direction of
conveyance of the sheet of paper so that its front and rear faces
may be printed on successively as the sheet of paper is conveyed.
And, the first sheet-fed duplex printer 2a at the most upstream
side is provided at its inlet side with an inlet side bridge roller
4 for guiding the sheet of paper from a paper feeder 3, and the
fourth sheet-fed duplex printer 2d at the most downstream side has
an output unit 5 connected to its outlet side, the output unit
comprising an outlet side bridge roller 5a and a delivery means
5b.
[0024] The sheet-fed duplex printers 2a to 2d are identical, in
makeup to each other and mention is made of their structure in
respect of the first sheet-fed duplex printer 2a shown in FIG.
2.
[0025] Numerals 6a and 6b designate a first and a second impression
cylinder having a diameter that is identical to each other. The
second impression cylinder 6b is positioned downstream in the
rotational direction of and obliquely below the first impression
cylinder 6a and is in rotational contact with the first impression
cylinder 6a. The first and second impression cylinders 6a and 6b
are synchronously driven to rotate so that the regions of
rotational contact thereof are both moved downwards.
[0026] The impression cylinders 6a and 6b are each provided on its
peripheral surface with a paper gripper (not shown) for gripping a
leading end portion of the sheet of paper fed from the rotational
upstream side. When the impression cylinders 6a and 6b are rotated,
the sheet of paper fed from upstream in rotational direction of the
first impression cylinder 6a is first gripped by the paper gripper
on the first impression cylinder 6a and conveyed following a
peripheral surface of the first impression cylinder 6a. The sheet
of paper drawn into between the first and second impression
cylinders 6a and 6b in a region of their rotational contact is then
gripped by the paper gripper on the second impression cylinder 6b,
the sheet of paper then traveling following a peripheral surface of
the second impression cylinder 6b. In the meantime, when the sheet
of paper moves over from the peripheral surface of the first
impression cylinder 6a to the peripheral surface of the second
impression cylinder 6b, its printing surface is reversed from the
front to the rear side.
[0027] A first electrophotographic printing unit 7a for front face
printing is disposed opposite to a peripheral surface area of the
first impression cylinder 6a which area is rotationally upstream of
the region of rotational contact between the two impression
cylinders 6a and 6b. And, a second electrophotographic printing
unit 7b for rear face printing is disposed opposite to a peripheral
surface area of the second impression cylinder 6b which area is
rotationally downstream of the region of rotational contact between
the two impression cylinders 6a and 6b.
[0028] The electrophotographic printing units 7a and 7b are
basically identical in structure to each other except that the
former and the latter are of a downwardly and an upwardly oriented
structure, respectively. Mention is made below of their structure
based on the electrophotographic printing unit for front face
printing 7a which is of a downwardly oriented structure.
[0029] The electrophotographic printing unit 7a is generally
identical in structure to one that is used as an ordinary
electrophotographic printer, having a photoconductor drum 8. Around
the photoconductor drum 8 over from its rotational upstream to
downstream sides, there are arranged a cleaning and de-charging or
static eliminating unit 9, a charging unit 10, an exposure unit 11,
a developing roller 13 in a developing unit 12, a carrier liquid
eliminating unit 14, these units being opposite to the periphery of
the photoconductor drum 8. The photoconductor drum 8 is in
rotational contact with a transfer roller 15, which is in turn in
rotational contact with the first impression cylinder 6a. Thus, a
toner image developed on the peripheral surface of the
photoconductor drum 8 by the developing roller 13 of the developing
unit 12 is transferred via the transfer roller 15 onto the sheet of
paper passing through a nip portion between the first impression
cylinder 6a and the transfer roller 15. Note further that a
transfer roller cleaning unit 16 is provided for the transfer
roller 15.
[0030] As for the upwardly oriented electrophotographic printing
unit 7b disposed at the underside of the second impression cylinder
6b, as in the downwardly oriented electrophotographic printing unit
7a a toner image transferred onto a transfer roller 15 from a
photoconductor drum 8 is transferred onto the sheet of paper
passing through a nip portion between the second impression
cylinder 6b and the transfer roller 15.
[0031] In the sheet-fed duplex printer 2a made up as mentioned
above, the sheet of paper fed from the inlet side bridge roller 4
of the paper feeder 3 is wound on the first impression cylinder 6a
and in that state is printed on its front face by the first
electrophotographic printing unit 7a. Then, the sheet of paper is
reversed in its printing side as it is wound on the second
impression cylinder 6b and in that state is printed on its rear
face by the second electrophotographic printing unit 7b. As a
result, a sheet of paper passed through the first sheet-fed duplex
printer 2a has a pattern printed on its both faces in one
color.
[0032] The sheet-fed duplex printers 2a to 2d made up as mentioned
above are arranged so that the first impression cylinder 6a in a
downstream (downstream in the direction of conveyance of the sheet
of paper) sheet-fed duplex printer is disposed in rotational
contact with the second impression cylinder 6b of its immediately
upstream (upstream in the direction of conveyance of the sheet of
paper) sheet-fed duplex printer. Thus, a sheet of paper fed into
the first sheet-fed duplex printer 2a will be printed on its both
faces and each in four colors as it is successively passed through,
and printed by, the sheet-fed duplex printers 2a to 2d and be lead
out into the output unit 5.
[0033] In the successive sheet-fed duplex printers 2a to 2d in this
case, a downstream positioned second impression cylinder 6b is
positioned obliquely below its immediately upstream first
impression cylinder 6a and a downstream positioned first impression
cylinder 6a is positioned obliquely upwards of its immediately
upstream second impression cylinder 6b. Thus, in the sheet-fed
duplex multi-color printer 1 having the sheet-fed duplex mono-color
printers 2a to 2d arranged as mentioned above, the impression
cylinders are arranged zigzag as shown in FIG. 1 over the
successive sheet-fed duplex printers 2a to 2d.
[0034] If mono-color printing of a sheet of paper is to be effected
on its both faces using a single first sheet-fed duplex printer 2a
alone, the second impression cylinder 6b may be provided with an
output unit 5 comprising an outlet side bridge roller 5a and a
delivery means 5b.
[0035] In the form of implementation mentioned above, each of the
sheet-fed duplex printers 2a to 2d has two impression cylinders 6a
and 6b disposed in rotational contact with each other. For example,
when simplex printing is effected with the first impression
cylinder 6a at the upstream side, the first impression cylinder 6a
constitutes a feed cylinder, the second impression cylinder 6b
constituting a bridge cylinder. And, the leading end of a sheet of
paper on which printing is initiated by the electrophotographic
printing unit 7a for the first impression cylinder 6a is fed from a
point of printing initiation A in FIG. 2 with the rotation of the
first impression cylinder 6a and taken over from a portion of
rotational contact B between the first and second impression
cylinders 6a and 6b to the second impression cylinder 6b for
movement as the second impression cylinder 6b is rotated. In the
meantime, the sheet of paper is printed on at the point A, and one
face of the sheet of paper is printed on in the sheet-fed duplex
printer 2a in such a way that when its leading end comes, e.g., to
a position C, ahead of a portion of rotational contact between the
second impression cylinder 6b in this sheet-fed duplex printer 2a
and the first impression cylinder 6a in the succeeding sheet-fed
duplex printer 2b, its trailing end passes through the point A.
[0036] Mention is made of an aspect of this one face printing with
reference to a diagrammatic view shown in FIG. 3. Note here that
the point of printing initiation A in this case is assumed to lie
at a top, highest point, of the first impression cylinder 6a.
[0037] In FIG. 3, let it be assumed that the first and second
impression cylinders 6a and 6b have a diameter of D, their axes are
horizontally spaced apart at a distance of 0.75D and the sheet of
paper has a length that is equal to a cylinders' peripheral length
of .pi.D. And, the leading end of the sheet of paper on which
printing is initiated at the point A is moved with rotation of the
first cylinder 6a by an angle of .theta..sub.1 to reach a point B
at which it is taken over to the second impression cylinder 6b. The
leading end of the sheet of paper is further moved with rotation of
the second impression cylinder 6b by an angle
.theta..sub.2=(360.degree.-.theta..sub.1) to reach a point C at
which time its trailing end is passed through the point A to
complete the one face or simplex printing.
[0038] Then, with the inter-axial spacing between the impression
cylinders 6a and 6b being 0.75D, it is seen that the angle
.theta..sub.1 is about 131.5 degrees, and with the length of the
sheet of paper being equal to the peripheral length of the
impression cylinder (360 degrees), it is seen that the angle
.theta..sub.2 between the points B and C is about 228.5 degrees.
The position C at which the trailing end of the sheet of paper then
lies is positioned slightly (7 degrees) over from just beside of
the second impression cylinder 6b. Thus, when the leading end of
the sheet of paper is moved by a distance of about 1.25D
horizontally, it follows that printing on one face of this sheet
over its total length has been completed.
[0039] FIG. 4 is an explanatory view illustrating a distance of
movement of a sheet of paper when one face of the sheet having a
length of D is printed over its total length with one impression
cylinder having a diameter of D. It is shown that movement of the
sheet of paper by the distance .pi.D makes the total length on its
one face printed.
[0040] In contrast, the form of implementation shown in FIG. 3
allows one face of a sheet of paper having a length of .pi.D to be
printed on over the total length when the sheet of paper is moved
by a distance of about 1.25D which is equal to about 1/2.5 of the
distance of movement in the case shown in FIG. 4. Thus, in a
printing apparatus in which one face of a sheet of paper having a
length equal to a peripheral length of the impression cylinder is
printed on over the total length, the apparatus can have a length
equal to about 1/2.5 of that of the makeup shown in FIG. 4.
[0041] In the form of implementation illustrated, when the leading
end of a sheet of paper comes, e.g., to a lowest point A' on the
second impression cylinder 6b, the second electrophotographic
printing unit 7b is driven to initiate printing on its rear face.
The leading end of the sheet of paper is moved and taken over to
the first impression cylinder 6a in the second sheet-fed duplex
printer 2b. When it is further moved to come to a point C' after
passing through a point A of the second front face printing
initiation on the first impression cylinder 6a, the trailing end of
the sheet of paper is passed through a point A' of rear face
printing initiation. At this time, printing on the rear face will
be completed.
[0042] In this way, a front and a rear face of a sheet of paper is
printed on in the first sheet-fed duplex printer 2a by moving the
sheet of paper from the point of front face printing initiation A
horizontally by a distance that is equal to about twice the
diameter D of the impression cylinders.
[0043] FIG. 5 shows an alternative form of implementation of the
present invention. A sheet-fed duplex multi-color printing
apparatus 1' according to this form of implementation is made up
having a first and a second sheet-fed duplex two-color printer 17a
and 17b arranged side by side. And, the first sheet-fed duplex
two-color printer 17a positioned upstream in a direction of
conveyance of a sheet of paper is provided at its inlet side with
an inlet side bridge roller 4 for guiding the sheet of paper from a
paper feeder 3, and the second sheet-fed duplex two-color printer
17b at the downstream side is provided at its outlet side with an
output unit 18 comprising a bridge roller 18a and a delivery means
18b. Also, the first and second sheet-fed duplex two-color printers
17a and 17b are interconnected via a first bridge roller 19a
disposed at downstream side of one and a second bridge roller 19b
disposed at upstream side of the other and driven in rotational
contact with the first bridge roller 19a.
[0044] The first and second sheet-fed duplex two-color printers 17a
and 17b are identical in structure to each other. Mention is made
of their structure with respect to the first sheet-fed duplex
two-color printer 17a.
[0045] There are shown a first and a second impression cylinder 20a
and 20b, which are identical in diameter to each other. The second
impression cylinder 20b is positioned downstream in a direction of
rotation of and obliquely below the first impression cylinder 20a
and is in rotational contact with the first impression cylinder
20a. The two impression cylinders 20a and 20b are synchronously
driven to rotate so that the regions of the rotational contact
thereof both move downwards.
[0046] The two impression cylinders 20a and 20b are each provided
on a peripheral surface thereof with a paper gripper (not shown)
for gripping a leading end portion of the sheet of paper fed from
its upstream side in a direction of the rotation. When the two
impression cylinders 20a and 20b are rotated, the sheet of paper
fed from the upstream side in the direction of rotation of the
first impression cylinder 20a is first gripped by the paper gripper
on the first impression cylinder 20a for conveyance following a
peripheral surface of the first impression cylinder 20a, and then
gripped in a region of rotational contact between the first and
second impression cylinders 20a and 20b by the paper gripper on the
second impression cylinder 20b for conveyance following a
peripheral surface of the second impression cylinder 20b. In the
meantime, when the sheet of paper moves over from the peripheral
surface of the first impression cylinder 20a to the peripheral
surface of the second impression cylinder 20b, its printing surface
is reversed from the front to the rear side
[0047] Opposite to a peripheral surface area of the first
impression cylinder 20a that is upstream of the region of
rotational contact between the first and second impression
cylinders 20a and 20b in the direction of rotation of the first
impression cylinder 20a, there are disposed a pair of
electrophotographic printing units 21a and 21b for front face
printing which are shifted in positions in the direction of
rotation of the first impression cylinder 20a. Opposite to a
peripheral surface area of the second impression cylinder 20b that
is downstream of the region of rotational contact between the first
and second impression cylinders 20a and 20b in the direction of
rotation of the second impression cylinder 20b, there are disposed
a pair of electrophotographic printing units 22a and 22b for rear
face printing which are shifted in position in the direction of
rotation of the second impression cylinder 20b.
[0048] The electrophotographic printing units 21a and 21b for front
face printing are each identical in structure to the
electrophotographic printing unit for front face printing 7a shown
in FIG. 2, and the electrophotographic printing units 22a and 22b
for rear face printing are each identical in structure to the
electrophotographic printing unit for rear face printing 7b shown
in FIG. 2.
[0049] A sheet of paper supplied, as guided by the inlet side
bridge roller 4, onto the rotating first impression cylinder 20a in
the first sheet-fed duplex two-color printer 17a is carried thereby
and printed on its front face in two colors by the two
electrophotographic printing units for front face printing 21a and
21b. The sheet of paper printed on its front face in the two colors
is then fed onto and carried by the rotating second impression
cylinder 20b in the first sheet-fed duplex two-color printer 17a
and printed on its rear face in two colors by the two
electrophotographic printing units for rear face printing 22a and
22b. The sheet of paper printed on the front and rear faces each in
the two colors in the first sheet-fed duplex two-color printer 17a
is taken over to the second sheet-fed duplex two-color printer 17b
via a first and a second bridge roller 19a and 19b and printed on
the front and rear faces each in a third and a fourth color.
[0050] The sheet-fed duplex two-color printers 17a, 17b in this
form of implementation of the invention are not limited to two in
number, but three or four such printers may be used as arranged
side by side.
[0051] In each of the forms of implementation as mentioned above,
using as printing means an electrophotographic printing unit other
than an offset rotary press with a printing plate mounted to a
printing cylinder for printing allows forming an image from digital
data on a photoconductor drum and cleaning of its surface after
image formation to proceed simultaneously and in succession and
hence allows printing of sheets of paper of sizes from small
(short) to large (long) regardless of the circular peripheral
length of a photoconductor drum.
[0052] Thus, unlike in the use of an offset press, if a pattern of
a size approximating the circular peripheral length of an
impression cylinder is to be printed, it is not essential that the
photoconductor drum and transfer roller be constructed to be equal
in diameter to the impression cylinder. Consequently, even for a
printed matter of large size (long) the impression cylinder (feed
cylinder) may be made up only having its circular peripheral length
to be an essential circular peripheral length, and it is possible,
too, to downsize the printing unit itself.
[0053] Also, the system used to convey a sheet of paper in the
forms of implementation mentioned above is designed to convey and
deliver while supporting and securing the sheet of paper upon
gripping with a paper gripper provided on a surface of each of the
two impression cylinders which function as a feed and bridge
cylinder. With the sheet of paper being always secured in position
with a paper gripper or grippers, it is possible to produce printed
sheets of paper at high speed and high accuracy.
[0054] Each of the impression cylinder may be provided on a
peripheral surface thereof with a plurality of paper grippers in a
direction of its peripheral length in relation to the size (length)
of a pattern to be printed and the peripheral length of the
impression cylinders. Also, it is possible to use a selected number
of grippers with unused grippers covered up with a covering member.
Further, the bridge rollers 4a, 5a, 19a and 19b in a form of
implementation as mentioned above may each be provided with a paper
gripper or grippers as needed. Each of these rollers may be
suitably altered in roller diameter to conform to the size of
printing in a form of implementation as mentioned above.
[0055] If a pattern to be duplex printed is varied in content, a
problem may arise that the surface of an impression cylinder tends
to be easily soiled. The problem, however, can be resolved by
coating the impression cylinder surface with a ceramic layer or
using the like known technique.
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